1. Field of the Invention
The invention relates to a microproportioning system for proportioning liquid volumes in the range of about one nanoliter to a few nanoliters.
2. Description of the Prior Art
In the proportioning systems which are known, a rough distinction is made between pipettes, dispensers, and multi-functional proportioners. All of the three groups are adapted to operate according to two different physical principles: The liquid proportioning process is either brought about by an air cushion or a direct displacement of the liquid takes place with no air cushion interposed. Further, a distinction is made from fixed-volume pipettes having an adjustable volume. The volumes being proportioned are between 0.5 μl and 2.500 μl.
Piston pipettes may be designed as fixed-volume pipettes or adjustable pipettes and operate in a volume range smaller than 1 μl up to 10 μl. The sample is drawn into a plastic syringe where it is separated by an air cushion from the piston in the pipette. Since the weight of the liquid column “is suspended” from the air cushion a pipette error will arise, which requires correction.
Pipettes or dispensers operating according to the direct-displacement principle do not exhibit these errors. They are specifically used in proportioning liquid at high steam pressures, high viscosities, high densities, and in molecular biology—e.g. in the polymerase chain reaction. They have tips or syringes with an integrated piston, which is coupled to a pipette driving means.
Multi-channel pipettes, dispensers, and electronic proportioning systems operate according to the aforementioned principles. Multi-channel pipettes may significantly reduce the number of required pipetting processes by several identical proportioning procedures. This is also the case for dispensers which stepwise dispense a liquid volume received and which also exist in a multi-channel design. Electronic pipettes and proportioning systems permit pipettings at a high reproducibility and have a wide field of application because of the dispensing function integrated. They operate in a volume range from 1 μl to 50 μl.
A precise, simple and low-cost proportioning of smaller liquid volumes would be desirable. Chemical analyses could then be made more precisely, more rapidly and at a lower cost, the latter also being made because of the lower consumption of media. This could enable novel routine diagnoses, e.g. in the field of medical care, or in environmental protection, which have been difficult to realize or have been too expensive hitherto. For applications in the field of biotechnology (e.g. in gene sequencing and genomic analysis) the informative content of examinations could be increased by an improvement of the proportioning quality. A substantial improvement of proportioning systems in the field of biotechnology might result, inter alia, in progress in breeding useful plants and useful animals and in controlling infectious diseases provoked by fungi, bacteria and viruses.
EP 0 725 267 A2 discloses a microproportioning system which has a micro-injection pump and a micro-diaphragm pump. To fill the system, the exit of the micro injection pump configured as a pipette tip may be dipped into a reservoir for the liquid being proportioned. The liquid is then delivered into the system by means of the micro-diaphragm pump, the entrance of which is connected to the micro-injection pump.
To clean the system, the exit of the micro-injection pump may be dipped into a stock for scouring liquid. The scouring liquid will also be delivered from the micro-diaphragm pump, the entrance of which is connected to the micro-injection pump, to a waste tank.
DE-A-41 40 533 relates to a microproportioning apparatus for the expulsion of minimal lubricant doses in the form of strands or droplets. A supply conduit for feeding the lubricant may open into the chamber of the apparatus at the side or the backward end of a tubular duct. The lubricating oil is drawn in via the supply conduit by deforming a bilaminar lamella. When an electric voltage is applied to a transducer the bilaminar lamella will bulge inwards and displace the lubricating oil so that the dose is expelled as droplets or a short strand through an outlet nozzle.
With this in view, it is the object of the invention to create a precise and simple microproportioning system having a proportioning volume in the range of a few nanoliters to a few microliters.